MR Perfusion Imaging in Acute Ischemic Stroke
Section snippets
The hemodynamics of ischemic stroke
The changes in perfusion that occur in acute stroke are driven fundamentally by global and/or regional changes in cerebral perfusion pressure (CPP).2 CPP is the difference between mean arterial pressure and venous pressure, the latter of which is usually equal to intracranial pressure. The cerebral vasculature responds to small reductions in CPP by dilating small arteries, thereby reducing cerebrovascular resistance, and successfully maintaining normal cerebral blood flow (CBF) over a wide
Dynamic susceptibility contrast imaging: basic physics and image acquisition
Because currently available techniques quantify the passage of blood through vessels that are too small to visualize directly with standard clinical MR imaging scanners, MR perfusion imaging must rely on detection of tracer agents within blood, rather than direct visualization of the vessels. This review focuses on dynamic susceptibility contrast (DSC) imaging, the technique that is used for MR perfusion imaging of acute stroke in most clinical centers. Arterial spin labeling (ASL)24 is another
Overview
Direct inspection of DSC images can yield rudimentary information about regional brain perfusion, and this approach is sometimes useful when severe patient motion precludes additional postprocessing. However, under most circumstances, individual DSC images like those in Fig. 1 undergo additional postprocessing to produce maps of various perfusion-related parameters, in which each pixel’s value reflects a single scalar measurement that is derived from the signal intensity-versus-time function
Diagnosis of Transient Ischemic Attack
DWI has become the gold standard for imaging detection of acute stroke, with sensitivity and specificity approaching 100%.34, 102, 103, 104, 105, 106, 107, 108 DWI’s unique ability to confirm or exclude the diagnosis of stroke can be of critical importance, because the etiology of stroke-like symptoms is not always initially clear.109 Establishing the diagnosis of cerebral ischemia can be especially difficult for transient ischemic attack (TIA) patients whose symptoms have resolved before the
Summary
In acute stroke, MR perfusion imaging can be used to measure a variety of different parameters, which provide differing and complementary information about regional brain perfusion. Interpretation of MR perfusion images requires a basic qualitative understanding of the various perfusion states that may coexist in the brain of an acute stroke patient, and should incorporate knowledge of several important artifacts that occur in perfusion imaging. MR perfusion imaging has been used successfully
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Drs Copen and Schaefer have no disclosures. Ona Wu has a patent on “Delay-compensated calculation of tissue blood flow,” US Patent 7,512,435. March 31, 2009, and the patent has been licensed to General Electric, Siemens, and Olea Medical.
This work was supported in part by grant R01 NS059775 from the National Institutes of Health.